Objectives of this research involve obtaining experimental evidence for the proposed model of meternal behavior by focussing on nesting during pregnancy and lactation. Preliminary work has indicated 3 general areas where further studies should be useful and productive: the genetic basis of maternal nesting, influence of the maternal nest on adult behavior of the offspring, and integration of maternal nesting in a thermoregulatory syndrome. Specific experiments will draw from and combine theories and design in quantitative genetics, ethology, and physiology to investigate these 3 areas. Genetic analyses designed to produce estimates of heritability, dominance variance, and maternal effects include the diallel cross, classical (Mendelian) analysis, parent-offspring regression, correlated response to selection, and inbreeding. Studies of the maternal influence will include tests for a critical period in development and analysis of the mediation of the influence on the young. Examination of the thermal relations associated with maternal nesting will rely on thermal preference to indicate differences in thermal perception, and examination of the influence of the insulative capacity of the nest as well as the total activity of the mother on the average temperature to which offspring are exposed.